This invention relates to the art of powder metallurgy and, more particularly, it relates to dispersion-strengthened and precipitation-strengthened metals. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
Alloys of tungsten in uranium are conventionally produced by coreducing UF.sub.4 with tungsten oxide or tungsten fluoride. The maximum amount of tungsten which can be alloyed with uranium to obtain a coherent shape using this coreducing process is about 4 wt %. Attempts to use larger amounts of tungsten result in production of a powder. It is believed that, prior to the present invention, no one has made coherent uranium alloys containing more than about 4 wt % tungsten in any significant or substantial quantity.
An alloy of this invention may be described as both a dispersion-strengthened and precipitation-strengthened metal. The strength of the inventive alloys is also increased by solid solution strengthening resulting from the tungsten dissolved in the uranium. Certain metals may be strengthened by adding to them relatively small quantities of particular materials in such a manner that the added materials do not substantially mix with the metal to form a homogenous phase, but are uniformly dispersed in particulate form throughout the metal. The material which is added may be referred to as a dispersoid, while the metal in which it is dispersed is referred to as the matrix metal; the combination is known as a dispersion-strengthened metal or a precipitation-strengthened metal.
A precipitation-strengthened metal is an alloy comprised of a matrix metal throughout which a dispersoid metal has been caused to be distributed by means of cooling a mixture of the dispersoid dissolved in the matrix such that particles of the dispersoid precipitate out. A dispersion-strengthened alloy is a matrix metal having a dispersoid metal distributed throughout it where the dispersoid has been caused to be distributed by means other than precipitation from the matrix metal upon cooling.
Oxides are the most common dispersoids because of their high hardness, stability at high temperature, insolubility in matrix metals, and availability in fine particulate form. However, in the present invention, the dispersoid is tungsten.
Additional information may be found in "Dispersion-Strengthened Materials," 7Powder Metallurgy, 9th Ed., Metals Handbook, American Society for Metals, 710-727 (1984).
Other major uses will be in applications requiring dense material and high mechanical strength.